1. Industrial Field of the Invention
The present invention relates to a ventilation line opening/closing means of a fuel tank which interrupts a ventilation line to a canister during fuel supply so as to restrict the fuel level when the tank is full (to prevent overfilling), and which opens the ventilation line during traveling of a vehicle.
2. Description of the Prior Art
Prevention of diffusion of automobile fuel into the atmosphere concerns the recent regulations for preventing air pollution, and is an important issue.
In a fuel tank of an automobile, vaporization of liquid fuel is activated by, for example, an increase in temperature, and accordingly, an internal pressure of the tank is increased. As the pressure becomes higher, there is more risk that fuel vapor will leak to the environment due to penetration or outflow, which results in air pollution as well as fuel loss. Moreover, when the tank internal pressure is high, there is more danger of a fire accident at the time of collision.
In order to release excessive fuel vapor into the canister, the resistance of the ventilation line is decreased to prevent the tank internal pressure from increasing. On the basis of this idea, various kinds of fuel vapor discharge valves and tank internal pressure control apparatus have been suggested, for example, as disclosed in U.S. Pat. Nos. 5,044,389, 5,044,397 and 5,065,782.